The role of fibrinogen D domain intermolecular association sites in the polymerization of fibrin and fibrinogen Tokyo II (gamma 275 Arg-->Cys)

A novel fibrinogen γ-chain frameshift mutation, p. Cys365Phefs*41, causing hypofibrinogenemia with bleeding phenotype in a Chinese family

Background

Congenital hypofibrinogenemia is a rare bleeding disease that is classified as the quantitative deficient type. In the present study, investigated the relationship between the genotype and phenotype in a family with hypofibrinogenemia.

Methods

The proband was aware of a predisposition to bleeding. Functional analysis was performed for her all family members, including coagulation function tests, thrombus molecular markers, thromboelastography, scanning electron microscopy, DNA sequencing, and high-performance liquid chromatography-mass spectrometry (HPLC-MS). Pathogenicity analysis and protein modeling of mutant amino acids were also performed.

Results

A novel heterozygous mutation in c.1094delG was detected in FGG exon 8, which resulted in p. Cys365Phefs*41 (containing the signal peptide) in the proband and her mother, who showed a corresponding decrease in fibrinogen function and levels. Thromboelastography indicated that the strength of their blood clots decreased and they had an increased risk of bleeding. The proband fibrin network structure was looser than healthy controls, with large pores in the network, which increased the permeability of lytic enzymes. Results of HPLC-MS showed a lack of mutant peptide chain expression in their plasma, indicating that the family had congenital hypofibrinogenemia, with a clinical phenotype that is related to the degree of fibrinogen deficiency. The mutation truncated the γ-peptide chain and destroyed the functional structure of fibrinogen, including the γ352Cys-γ365Cys disulfide bond. The truncated peptide chains may also lead to nonsense-mediated decay.

Conclusions

The mutation induced a structural change at the carboxyl-terminal of the fibrinogen molecule, leading to fibrinogen secretion dysfunction.

Automated screening procedure for the phenotypes of congenital fibrinogen disorders using novel parameters, |min1|c and Ac/|min1|c, obtained from clot waveform analysis using the Clauss method

INTRODUCTION

Fibrinogen activity (Ac) is widely measured, but fibrinogen antigen (Ag) is measured only in specialized laboratories, so it is difficult to discriminate congenital fibrinogen disorders (CFDs) from acquired hypofibrinogenemia (aHypo). In this study, to screen for CFD phenotypes we adopted novel parameters, |min1|c and Ac/ |min1|c, and compared these with validated Ac, Ag, and Ac/Ag, and previously proposed Ac/dH and Ac/|min1|.

MATERIALS AND METHODS

We calibrated |min1| using a CN-6000 instrument and investigated the correlation between Ag and |min1|c for aHypo (n = 131) and CFD [18 dysfibrinogenemia (Dys), two hypodysfibrinogenemia (Hypodys) and four hypofibrinpogenemia (Hypo)]. Furthermore, we proposed a schema for screening CFD phenotypes using |min1|c and Ac/|min1|c.

RESULTS

The |min1|c correlated well with Ag in aHypo, and Ac/|min1|c was a better parameter for screening Dys and Hypodys than Ac/dH and Ac/|min1|. With the combination of |min1|c and Ac/|min1|c parameters, 15 Dys, 2 Hypodys and four Hypo were categorized in agreement with the phenotype determined using Ag and Ac/Ag; conversely three Dys were classified as one Hypodys (AαR16C) and two Hypo (BβG15C).

CONCLUSION

We demonstrated that |min1|c and Ac/|min1|c are valuable parameters for screening CFD patients and phenotypes in laboratories that do not measure Ag or perform genetic analysis.

Recombinant γY278H Fibrinogen Showed Normal Secretion from CHO Cells, but a Corresponding Heterozygous Patient Showed Hypofibrinogenemia

We identified a novel heterozygous hypofibrinogenemia, γY278H (Hiroshima). To demonstrate the cause of reduced plasma fibrinogen levels (functional level: 1.12 g/L and antigenic level: 1.16 g/L), we established γY278H fibrinogen-producing Chinese hamster ovary (CHO) cells. An enzyme-linked immunosorbent assay demonstrated that synthesis of γY278H fibrinogen inside CHO cells and secretion into the culture media were not reduced. Then, we established an additional five variant fibrinogen-producing CHO cell lines (γL276P, γT277P, γT277R, γA279D, and γY280C) and conducted further investigations. We have already established 33 γ-module variant fibrinogen-producing CHO cell lines, including 6 cell lines in this study, but only the γY278H and γT277R cell lines showed disagreement, namely, recombinant fibrinogen production was not reduced but the patients’ plasma fibrinogen level was reduced. Finally, we performed fibrinogen degradation assays and demonstrated that the γY278H and γT277R fibrinogens were easily cleaved by plasmin whereas their polymerization in the presence of Ca²⁺ and “D:D” interaction was normal. In conclusion, our investigation suggested that patient γY278H showed hypofibrinogenemia because γY278H fibrinogen was secreted normally from the patient’s hepatocytes but then underwent accelerated degradation by plasmin in the circulation.

Mutations Causing Mild or No Structural Damage in Interfaces of Multimerization of the Fibrinogen γ-Module More Likely Confer Negative Dominant Behaviors

Different pathogenic variants in the same protein or even within the same domain of a protein may differ in their patterns of disease inheritance, with some of the variants behaving as negative dominant and others as autosomal recessive mutations. Here is presented a structural analysis and comparison of the molecular characteristics of the sites in fibrinogen γ-module, a fibrinogen component critical in multimerization processes, targeted by pathogenic variants (HGMD database) and by variants found in the healthy population (gnomAD database). The main result of this study is the identification of the molecular pathogenic mechanisms defining which pattern of disease inheritance is selected by mutations at the crossroad of autosomal recessive and negative dominant modalities. The observations in this analysis also warn about the possibility that several variants reported in the non-pathogenic gnomAD database might indeed be a hidden source of diseases with autosomal recessive inheritance or requiring a combination with other disease-causing mutations. Disease presentation might remain mostly unrevealed simply because the very low variant frequency rarely results in biallelic pathogenic mutations or the coupling with mutations in other genes contributing to the same disease. The results here presented provide hints for a deeper search of pathogenic mechanisms and modalities of disease inheritance for protein mutants participating in multimerization phenomena.

Identification and characterization of novel mutations in Chinese patients with congenital fibrinogen disorders

INTRODUCTION

Congenital fibrinogen disorders are characterized by heterogeneous clinical manifestations with mutations in the fibrinogen gene cluster. We aimed to describe the molecular genetics and clinical manifestations of fibrinogen abnormalities and perform genotype-phenotype correlations.

MATERIALS AND METHODS

Genetic analysis of fibrinogen genes was performed by direct sequencing. The effect of the specific missense variants on fibrinogen structure and function was analyzed using PROVEAN and PolyPhen-2 algorithms and was predicted by protein modeling.

RESULTS

Thirteen mutations, including five novel mutations, were identified in the three fibrinogen genes. There was poor correlation between genotypes and phenotypes. All but one of the novel mutations in subjects were predicted to be deleterious. Protein modeling predicted that multiple ienteractions with surrounding residues for novel variants were likely to result in congenital fibrinogen disorders.

CONCLUSION

This study in a relatively large cohort of Chinese patients with congenital fibrinogen disorders enabled the identification of five new fibrinogen missense mutations. In silico modeling may represent a valuable tool for understanding amino acid residues from novel variants leading to congenital fibrinogen disorders, but it should be followed by functional studies. Clinical presentation of fibrinogen disorders was variable, possibly due to genetic and environmental modifiers.

Heterozygous variant fibrinogen γA289V (Kanazawa III) was confirmed as hypodysfibrinogenemia by plasma and recombinant fibrinogens

INTRODUCTION

Congenital fibrinogen disorders are classified as afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia. However, difficulties are associated with discriminating between dysfibrinogenemia, hypofibrinogenemia, and hypodysfibrinogenemia using routine analyses. We previously reported a heterozygous variant fibrinogen (γA289V; Kanazawa III) as hypodysfibrinogenemia; however, the same variant had previously been described as hypofibrinogenemia. To clarify the production of γA289V fibrinogen, we expressed recombinant γA289V (r-γA289V) fibrinogen and compared it with wild-type (WT) and adjacent recombinant variant fibrinogens.

METHODS

Target mutations were introduced into a fibrinogen γ-chain expression vector by site-directed mutagenesis, and the vector was then transfected into Chinese hamster ovary cells to produce recombinant fibrinogen. Fibrinogen was purified from the plasma of the proposita, and culture media and fibrinogen functions were analyzed using fibrin polymerization, plasmin protection, and FXIIIa-catalyzed fibrinogen cross-linking.

RESULTS

The fibrinogen concentration ratio of the culture media to cell lysates was markedly lower for r-γA289V fibrinogen than for WT. Because the secretion of recombinant γF290L (r-γF290L) fibrinogen was similar to WT, we compared r-γF290L fibrinogen functions with WT. The fibrin polymerization of Kanazawa III plasma (K-III) fibrinogen was significantly weaker than normal plasma fibrinogen. Moreover, K-III fibrinogen showed a markedly reduced "D:D" interaction. However, all functions of r-γF290L fibrinogen were similar to WT. An in silico analysis confirmed the above results.

CONCLUSION

The present results demonstrated that γA289 is crucial for the γ-module structure, and the γA289V substitution markedly reduced fibrinogen secretion. Moreover, K-III fibrinogen showed markedly reduced fibrin polymerization and "D:D" interactions. γA289V fibrinogen was confirmed as hypodysfibrinogenemia.

γD318Y fibrinogen shows no fibrin polymerization due to defective "A-a" and "B-b" interactions, whereas that of γK321E fibrinogen is nearly normal

BACKGROUND

The fibrinogen γ-module has several functional sites and plays a role in dysfibrinogenemia, which is characterized by impaired fibrin polymerization. Variants, including γD318Y and γΔN319D320, have been reported at the high affinity Ca²⁺-binding site, and analyses using recombinant fibrinogen revealed the importance of this site for fibrinogen functions and secretion. We examined the polymerization abilities of the recombinant fibrinogen variants, γD318Y and γK321E.

MATERIALS AND METHODS

γD318Y and γK321E were produced using CHO cells and fibrinogen functions were examined using thrombin- or batroxobin-catalyzed polymerization, gel chromatography, protection against plasmin degradation, and factor XIIIa cross-linking.

RESULTS

γD318Y did not show any polymerization by thrombin or batroxobin, similar to γΔN319D320, whereas γK321E had slightly impaired polymerization. The functions of Ca²⁺ binding, hole 'a', and the "D-D" interaction were markedly reduced in γD318Y, and gel chromatography suggested altered protofibril formation. In silico analyses revealed that structural changes in the γ-module of these variants were inconsistent with polymerization results. The degree of structural changes in γD318Y was moderate relative to those in γD318A and γD320A, which had markedly impaired polymerization, and γK321E, which showed slightly impaired polymerization.

CONCLUSION

Our results suggest that no polymerization of γD318Y or γΔN319D320 was due to the loss of both "A-a" and "B-b" interactions. Previous studies demonstrated that "B-b" interaction alone causes polymerization of neighboring γD318A and γD320A fibrinogen, which is subsequently decreased. Marked changes in the tertiary structure of the γD318Y γ-module influenced the location and/or orientation of the adjacent β-module, which led to impaired "B-b" interactions.

Attenuation of Thrombin-Mediated Fibrin Formation via Changes in Fibrinogen Conformation Induced by Reaction with S-nitroso-N-acetylpenicillamine, but not S-nitrosoglutathione

Previous work in a 4 h rabbit thrombogenicity model has shown that a nitric oxide- (NO) generating polymer extracorporeal circuits (ECC) with infusion of S-nitroso-N-acetyl-penicillamine (SNAP) preserved platelets eventhough platelets were activated as shown by an increase in the glycoprotein, p-selectin. The platelet preservation mechanism was shown to be due to a changing fibrinogen structure leading to attenuation of platelet aggregation. Understanding the effects that SNAP, another RSNO, S-nitroso-glutathione (GSNO) as well as the non-RSNO, sodium nitroprusside (SNP), may have on human fibrinogen polymerization, this in vitro study evaluated the released NO effects on the thrombin-mediated fibrin formation and fibrinogen structure. Thrombin-induced fibrin formation at 300 μM SNAP (50 + 11% of baseline) was significantly reduced compared to SNAP's parent, N-acetyl-penicillamine (NAP) (95 + 13%) after 1 h of RSNO exposure. GSNO, its parent, glutathione (GSH) and 1000 ppm NO gas did not attenuate the thrombin-mediated fibrin formation. SNAP, NAP and SNP exposure for 1 h, however, did not decrease thrombin activity by directly inhibiting thrombin itself. Changes in fibrinogen conformation as measured by intrinsic tryptophan fluorescence significantly decreased in the 300 μM SNAP (38057 + 1196 mean fluorescence intensity (MFI) and SNP (368617 + 541 MFI) groups versus the NAP control (47937 + 1196 MFI). However, infused 1000 ppm NO gas had no direct effect on the ITF after 1 h incubation at 37°C. High performance liquid chromatography (HPLC) showed that fibrinogen degradation by 0.03 U/ml thrombin was concentration-dependently reduced after 1 h with SNAP but not with NAP or SNP. Western blotting showed RSNOs, SNAP, NAP and the non-RSNO, SNP-incubated fibrinogen solutions showed that the percent level of the Aγ dimer to total Aγ dimer + γ monomer was significantly reduced in the case of the SNAP group when compared to SNP group. These results suggest that NO donors such as SNAP and SNP induce fibrinogen conformational changes by potentially nitrosating fibrinogen tyrosine residues. These NO-mediated fibrinogen changes induced via NO donors may provide another mechanism of NO for improving thromboresistance in ECC.

The amplitude of coagulation curves from thrombin time tests allows dysfibrinogenemia caused by the common mutation FGG-Arg301 to be distinguished from hypofibrinogenemia

INTRODUCTION

Thrombin time (TT) tests are useful for diagnosing coagulation disorders involving abnormal fibrinogen but do not allow us to distinguish between qualitative and quantitative defects. However, with the widening availability of optical coagulation automates, more information about the coagulation process is becoming increasingly accessible.

METHODS

In this study, we compared the coagulation curves of TT tests carried out with plasma from healthy donors with those from patients with acquired low Clauss fibrinogen levels or with dysfibrinogenemia caused by a heterozygous point mutation in the fibrinogen γ-chain that results in a p.Arg301(275)Cys substitution. The functional fibrinogen levels of these three groups of samples were also measured with the Clauss method, and their fibrinogen protein levels were determined by ELISA.

RESULTS

Our data indicate that the amplitude and maximal velocity of coagulation curves from plasma samples from FGG p.Arg301(275)Cys dysfibrinogenemic patients were comparable to those from plasma samples with fibrinogen in the normal range, whereas the amplitude of coagulation curves from patients with acquired low fibrinogen levels was lower.

CONCLUSIONS

Examination of the amplitude of coagulation curves generated during TT tests may provide additional information to enable the differential diagnoses of diseases following a low fibrinogen measurement by the Clauss method.

The strengthening role of D:D interactions in fibrin self-assembly under oxidation

The effect on ozone-induced oxidation on the self-assembly of fibrin in the presence of fibrin-stabilizing factor FXIIIa of soluble cross-linked fibrin oligomers was studied in a medium containing moderate urea concentrations. It is established that fibrin oligomers were formed by the protofibrils cross-linked through γ-γ dimers and the fibrils additionally cross-linked by through α-polymers. The oxidation promoted both the accumulation of greater amounts of γ-γ dimers and the formation of protofibrils, fibrils, and their dissociation products emerging with increasing urea concentrations, which have a high molecular weight. It is concluded that the oxidation enhances the axial interactions between D-regions of fibrin molecules.

Dysfibrinogenemia: from molecular anomalies to clinical manifestations and management

Congenital dysfibrinogenemia is a qualitative congenital fibrinogen disorder characterized by normal antigen levels of a dysfunctional fibrinogen. The diagnosis is usually based on discrepancies between fibrinogen activity and antigen levels, but could require more specialized techniques for the assessment of fibrinogen function, owing to some limitations in routine assays. Molecular abnormalities, which are frequently heterozygous missense mutations localized in exon 2 of FGA and exon 8 of FGG, lead to defects in one or more phases of fibrinogen to fibrin conversion, fibrin network formation, and other important functions of fibrinogen. The clinical phenotype is highly heterogeneous, from no manifestations to bleeding and/or thrombotic events. Asymptomatic propositi and relatives with the predisposing genotype are at risk of developing adverse outcomes during the natural course of the disease. Correlations between genotype and phenotype have not yet been clearly established, with the exception of some abnormal fibrinogens that severely increase the risk of thrombosis. Functional analysis of polymerization and fibrinolysis, structural studies of the fibrin network and the viscoelastic properties of fibrin clot could help to predict the phenotype of congenital dysfibrinogenemia, but have not yet been evaluated in detail. The management is essentially based on personal and family history; however, even individuals who are still asymptomatic and without a family history should be carefully assessed and monitored. Particular situations, such as pregnancy, delivery, and surgery, require a multidisciplinary approach.

A dysfibrinogenemia leading to resistance to bovine thrombin

INTRODUCTION

A 26-year-old woman presented to our institute for a routine check-up. Nothing was abnormal excepted a prolonged Thrombin Time and a low fibrinogen concentration determined by the Clauss method. Fibrinogen concentration was then measured by PT-derived method, and revealed normal levels. This was therefore suggestive for a dysfibrinogenemia. The patient had no history of haemostatic problems and was under no medication. Her family history revealed nothing relevant, but death of her father from a cerebrovascular accident.

METHODS AND RESULTS

Complementary tests were performed: Platelet Function Assay, Factor VIII coagulant activity, von Willebrand antigen quantification, Ristocetin Cofactor activity, thromboelastogram and euglobulin lysis time were all within normal ranges. Finally, thrombin time and Clauss fibrinogen using a human thrombin instead of a bovine thrombine revealed normal results. DNA was then extracted for sequencing the genes coding for fibrinogen. This revealed the presence of a substitution Arg>Cys in position 275 of the γ-chain of the fibrinogen.

DISCUSSION

This mutation has already been reported in the literature with four cases of thrombosis, three cases of haemorrhage and eight had no clinical signs. The gamma chain is implicated in several crucial interactions such as the primary polymerization 'a', the binding to calcium, the factor XIIIa-induced cross-linking, the binding to plasminogen and to tissue plasminogen activator. Results of the literature show that this mutation has several impacts on in vitro tests, and we proved that those can be corrected by the use of human thrombin.

Ozone-induced oxidative modification of fibrinogen: role of the D regions

Native fibrinogen is a key blood plasma protein whose main function is to maintain hemostasis by virtue of producing cross-linked fibrin clots under the influence of thrombin and fibrin-stabilizing factor (FXIIIa). The aim of this study was to investigate mechanisms of impairment of both the molecular structure and the spatial organization of fibrinogen under ozone-induced oxidation. FTIR analysis showed that ozone treatment of the whole fibrinogen molecule results in the growth of hydroxyl, carbonyl, and carboxyl group content. A similar analysis of fibrinogen D and E fragments isolated from the oxidized protein also revealed transformation of distinct important functional groups. In particular, a remarkable decay of N-H groups within the peptide backbone was observed along with a lowering of the content of C-H groups belonging to either the aromatic moieties or the aliphatic chain CH2 and CH3 units. The model experiments performed showed that the rather unexpected decay of the aliphatic CH units might be caused by the action of hydroxyl radicals, these being produced in the water solution from ozone. The observed dissimilarities in the shapes of amide I bands of the fibrinogen D and E fragments before and after ozone treatment are interpreted in terms of feasible local conformational changes affecting the secondary structure of the protein. Taken as a whole, the FTIR data suggests that the terminal D fragments of fibrinogen are markedly more susceptible to the ozone-induced oxidation than the central E fragment. The data on elastic and dynamic light scattering provide evidence that, in the presence of FXIIIa, both the unoxidized and the oxidized fibrinogen molecules bind to one another in an "end-to-end" fashion to form the flexible covalently cross-linked fibrinogen homopolymers. The γ and α polypeptide chains of the oxidized fibrinogen proved to be involved in the enzymatic cross-linking more readily than those of unaffected fibrinogen. The experimental data on fibrinogen oxidation acquired in the present study, combined with our earlier findings, make it reasonable to suppose that the spatial structure of fibrinogen could be evolutionarily adapted to some reactive oxygen species actions detrimental to the protein function.

Recombinant γT305A fibrinogen indicates severely impaired fibrin polymerization due to the aberrant function of hole 'A' and calcium binding sites

INTRODUCTION

We examined a 6-month-old girl with inherited fibrinogen abnormality and no history of bleeding or thrombosis. Routine coagulation screening tests showed a markedly low level of plasma fibrinogen determined by functional measurement and also a low level by antigenic measurement (functional/antigenic ratio=0.295), suggesting hypodysfibrinogenemia.

MATERIALS AND METHODS

DNA sequence analysis was performed, and γT305A fibrinogen was synthesized in Chinese hamster ovary cells based on the results. We then functionally analyzed and compared with that of nearby recombinant γN308K fibrinogen.

RESULTS

DNA sequence analysis revealed a heterozygous γT305A substitution (mature protein residue number). The γT305A fibrinogen indicated markedly impaired thrombin-catalyzed fibrin polymerization both in the presence or absence of 1mM calcium ion compared with that of γN308K fibrinogen. Protection of plasmin degradation in the presence of calcium ion or Gly-Pro-Arg-Pro peptide (analogue for so-called knob 'A') and factor XIIIa-catalyzed fibrinogen crosslinking demonstrated that the calcium binding sites, hole 'a' and D:D interaction sites were all markedly impaired, whereas γN308Kwas impaired at the latter two sites. Molecular modeling demonstrated that γT305 is localized at a shorter distance than γN308 from the high affinity calcium binding site and hole 'a'.

CONCLUSION

Our findings suggest that γT305 might be important for construction of the overall structure of the γ module of fibrinogen. Substitution of γT305A leads to both dysfibrinogenemic and hypofibrinogenemic characterization, namely hypodysfibrinogenemia. We have already reported that recombinant γT305A fibrinogen was synthesized normally and secreted slightly, but was significantly reduced.

Severe bleeding in a woman heterozygous for the fibrinogen gammaR275C mutation

The dysfibrinogen gammaR275C can be a clinically silent mutation, with only two out of 17 cases in the literature reporting a hemorrhagic presentation and four cases reporting a thrombotic presentation. We describe here a particularly severe presentation in 54-year-old female patient who required a hysterectomy at 47 years of age due to heavy menstrual bleeding. Coagulation studies revealed a prolonged prothrombin time and thrombin time, a normal fibrinogen antigen level, and a low fibrinogen activity level. Molecular analysis of the patient's DNA revealed a gamma chain gene mutation resulting in an amino acid substitution at residue 275 (gammaR275C). Protein sequencing of the fibrinogen gamma chain confirmed this mutation, which was named Fibrinogen Portland I. This case demonstrates that the gammaR275C mutation can lead to a severe hemorrhagic phenotype.

Role of fibrin structure in thrombosis and vascular disease

Fibrin clot formation is a key event in the development of thrombotic disease and is the final step in a multifactor coagulation cascade. Fibrinogen is a large glycoprotein that forms the basis of a fibrin clot. Each fibrinogen molecule is comprised of two sets of Aα, Bβ, and γ polypeptide chains that form a protein containing two distal D regions connected to a central E region by a coiled-coil segment. Fibrin is produced upon cleavage of the fibrinopeptides by thrombin, which can then form double-stranded half staggered oligomers that lengthen into protofibrils. The protofibrils then aggregate and branch, yielding a three-dimensional clot network. Factor XIII, a transglutaminase, cross-links the fibrin stabilizing the clot protecting it from mechanical stress and proteolytic attack. The mechanical properties of the fibrin clot are essential for its function as it must prevent bleeding but still allow the penetration of cells. This viscoelastic property is generated at the level of each individual fiber up to the complete clot. Fibrinolysis is the mechanism of clot removal, and involves a cascade of interacting zymogens and enzymes that act in concert with clot formation to maintain blood flow. Clots vary significantly in structure between individuals due to both genetic and environmental factors and this has an effect on clot stability and susceptibility to lysis. There is increasing evidence that clot structure is a determinant for the development of disease and this review will discuss the determinants for clot structure and the association with thrombosis and vascular disease.

Fibrinogen nanofibril growth and self-assembly on Au (1,1,1) surface in the absence of thrombin

Fibrinogen (fg) molecules were observed to form very well organized patterns of nanofibrils by self-assembling on Au (1,1,1) surface without any addition of thrombin, growing in two orientations (longitude and transverse). This observation is new and unique for gold surfaces, in contrast with Mica or HOPG surfaces. Based on the experimental results, we proposed an assembly mechanism: Au-S interactions and its activated interactions in the ‘αC-domain’ are two main causes for the patterned assembly on Au(1,1,1) surface, and ‘D: D’ and ‘γXL’ interactions help the elongation and strengthening of the fibril assembly.

Nanoscale probing reveals that reduced stiffness of clots from fibrinogen lacking 42 N-terminal Bbeta-chain residues is due to the formation of abnormal oligomers

Removal of Bbetal-42 from fibrinogen by Crotalus atrox venom results in a molecule lacking fibrinopeptide B and part of a thrombin binding site. We investigated the mechanism of polymerization of desBbeta1-42 fibrin. Fibrinogen trinodular structure was clearly observed using high resolution noncontact atomic force microscopy. E-regions were smaller in desBbeta1-42 than normal fibrinogen (1.2 nm +/- 0.3 vs. 1.5 nm +/- 0.2), whereas there were no differences between the D-regions (1.7 nm +/- 0.4 vs. 1.7 nm +/- 0.3). Polymerization rate for desBbeta1-42 was slower than normal, resulting in clots with thinner fibers. Differences in oligomers were found, with predominantly lateral associations for desBbeta1-42 and longitudinal associations for normal fibrin. Clot elasticity as measured by magnetic tweezers showed a G' of approximately 1 Pa for desBbeta1-42 compared with approximately 8 Pa for normal fibrin. Spring constants of early stage desBbeta1-42 single fibers determined by atomic force microscopy were approximately 3 times less than normal fibers of comparable dimensions and development. We conclude that Bbeta1-42 plays an important role in fibrin oligomer formation. Absence of Bbeta1-42 influences oligomer structure, affects the structure and properties of the final clot, and markedly reduces stiffness of the whole clot as well as individual fibrin fibers.

Fibrinogen Hershey IV: a novel dysfibrinogen with a gammaV411I mutation in the integrin alpha(IIb)beta(3) binding site

The carboxyl terminal segment of the fibrinogen gamma chain from gamma408-411 plays a crucial role in platelet aggregation via interactions with the platelet receptor alpha(IIb)beta(3). We describe here the first naturally-occurring fibrinogen point mutation affecting this region and demonstrate its effects on platelet interactions. DNA sequencing was used to sequence the proband DNA, and platelet aggregation and direct binding assays were used to quantitate the biological effects of fibrinogen Hershey IV. The Hershey IV proband was found to be heterozygous for two mutations, gammaV411I and gammaR275C. Little difference in aggregation was seen when fibrinogen Hershey IV was compared to normal fibrinogen. However, less aggregation inhibition was observed using a competing synthetic dodecapeptide containing the V411I mutation as compared to the wild-type dodecapeptide. Purified fibrinogen Hershey IV also bound to purified platelet alpha(IIb)beta(3) with a lower affinity than wild-type fibrinogen. These findings show that the gammaV411I mutation results in a decreased ability to bind platelets. In the heterozygous state, however, the available wild-type fibrinogen appears to be sufficient to support normal platelet aggregation.

Changes in fibrinogen and fibrin induced by a peptide analog of fibrinogen gamma365-380

BACKGROUND

The effects of synthetic peptides with sequences derived from the gamma-chain of fibrinogen on the functional properties of fibrinogen and fibrin were investigated.

METHODS

Methods included thrombelastography, clot turbidity measurement, clot elasticity measurement, platelet aggregation, and scanning transmission electron microscopy (STEM).

RESULTS

Peptide gamma369-380 (NH(2)-WATWKTRWYSMK-COOH) showed the greatest impact on fibrin structure, compared with the 76 other overlapping dodecapeptides. Addition of this peptide, or peptide gamma365-380 (NH(2)-NGIIWATKTREWYSMK-COOH) to a mixture of fibrinogen and thrombin resulted a shorter clotting time, higher clot turbidity, lower clot elastic modulus, a higher degree of D-trimer and D-tetramer formation, and impaired plasmin proteolysis of the clot. In STEM, fibrin formed in the presence of peptide gamma369-380 consisted of a more extensive array of linear fibrils typically consisting of 20 or more molecules. Fibrils were better organized than those from non-peptide containing mixtures.

CONCLUSIONS

Replacement of the tryptophan residue gamma376 massively reduced the effect of the peptide on fibrin structure. Binding of the peptide to fibrinogen induces conformational changes, which result in accelerated clotting and increased lateral association of fibrin protofibrils. The results imply a relevant functional role of sites interacting with peptide gamma369-380 region in the fibrinogen molecule.

Decorin Modulates Fibrin Assembly and Structure

Emerging evidence indicates that fibrin clotting is regulated by different external factors. We demonstrated recently that decorin, a regulator of collagen fibrillogenesis and transforming growth factor-beta activity, binds to the D regions of fibrinogen (Dugan, T.A., Yang, V. W.-C., McQuillan, D.J., and Höök, M. (2003) J. Biol. Chem. 278, 13655-13662). We now report that the decorin-fibrinogen interaction alters the assembly, structure, and clearance of fibrin fibers. Relative to fibrinogen, substoichiometric amounts of decorin core protein modulated clotting, whereas an excess of an active decorin peptide was necessary for similar activity. These concentration-dependent effects suggest that decorin bound to the D regions sterically modulates fibrin assembly. Scanning electron microscopy images of fibrin clotted in the presence of increasing concentrations of decorin core protein showed progressively decreasing fiber diameter. The sequestration of Zn(2+) ions from the N-terminal fibrinogen-binding region abrogated decorin incorporation into the fibrin network. Compared with linear thicker fibrin fibers, the curving thin fibers formed with decorin underwent accelerated tissue-type plasminogen activator-dependent fibrinolysis. Collectively, these data demonstrate that decorin can regulate fibrin organization and reveal a novel mechanism by which extracellular matrix components can participate in hemostasis, thrombosis, and wound repair.

A classification of the fibrin network structures formed from the hereditary dysfibrinogens

OBJECTIVE

The main objective was to study the relationships of the molecular defects in 38 dysfibrinogens with their fibrin networks.

METHODS AND RESULTS

Scanning electron microscopic analyses revealed that all the fibrins formed under the same conditions had networks composed of either normal thickness fibers or thin fibers, accompanied by a variety of alterations in the network structure and characteristics. We classified these fibrin networks into five classes, designated normal, less-ordered, porous A, porous B and lace-like networks. The dysfibrinogens with defects in fibrinopeptide A release or the E:D binding sites formed normal or less-ordered networks, while those with defects in the D:D association formed porous A networks composed of many tapered terminating fibers, despite having fibers of normal width, and containing many pores or spaces. The porous B and lace-like networks were composed of highly branched thin fibers because of defects in the lateral association among protofibrils, and the major difference between them was the porosity of the porous B networks. All the porous B networks were easily damaged by mechanical stress, whereas the lace-like networks retained high resistance to such stress, indicating that the network strength was not dependent on the fiber width, but on the porosity that led to fragility of the network.

CONCLUSION

Impairment of the D:D association is the major disturbing factor that leads to the formation of porous fibrin networks. The porosity may be introduced by severe impairment of the D:D association, as well as the lateral association, as has often been observed by extra glycosylation or defects in Ca2+ binding.

Fibrinogen and fibrin structure and functions

Fibrinogen molecules are comprised of two sets of disulfide-bridged Aalpha-, Bbeta-, and gamma-chains. Each molecule contains two outer D domains connected to a central E domain by a coiled-coil segment. Fibrin is formed after thrombin cleavage of fibrinopeptide A (FPA) from fibrinogen Aalpha-chains, thus initiating fibrin polymerization. Double-stranded fibrils form through end-to-middle domain (D:E) associations, and concomitant lateral fibril associations and branching create a clot network. Fibrin assembly facilitates intermolecular antiparallel C-terminal alignment of gamma-chain pairs, which are then covalently 'cross-linked' by factor XIII ('plasma protransglutaminase') or XIIIa to form 'gamma-dimers'. In addition to its primary role of providing scaffolding for the intravascular thrombus and also accounting for important clot viscoelastic properties, fibrin(ogen) participates in other biologic functions involving unique binding sites, some of which become exposed as a consequence of fibrin formation. This review provides details about fibrinogen and fibrin structure, and correlates this information with biological functions that include: (i) suppression of plasma factor XIII-mediated cross-linking activity in blood by binding the factor XIII A2B2 complex. (ii) Non-substrate thrombin binding to fibrin, termed antithrombin I (AT-I), which down-regulates thrombin generation in clotting blood. (iii) Tissue-type plasminogen activator (tPA)-stimulated plasminogen activation by fibrin that results from formation of a ternary tPA-plasminogen-fibrin complex. Binding of inhibitors such as alpha2-antiplasmin, plasminogen activator inhibitor-2, lipoprotein(a), or histidine-rich glycoprotein, impairs plasminogen activation. (iv) Enhanced interactions with the extracellular matrix by binding of fibronectin to fibrin(ogen). (v) Molecular and cellular interactions of fibrin beta15-42. This sequence binds to heparin and mediates platelet and endothelial cell spreading, fibroblast proliferation, and capillary tube formation. Interactions between beta15-42 and vascular endothelial (VE)-cadherin, an endothelial cell receptor, also promote capillary tube formation and angiogenesis. These activities are enhanced by binding of growth factors like fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF), and cytokines like interleukin (IL)-1. (vi) Fibrinogen binding to the platelet alpha(IIb)beta3 receptor, which is important for incorporating platelets into a developing thrombus. (vii) Leukocyte binding to fibrin(ogen) via integrin alpha(M)beta2 (Mac-1), which is a high affinity receptor on stimulated monocytes and neutrophils.

Functional analysis of recombinant Bbeta15C and Bbeta15A fibrinogens demonstrates that Bbeta15G residue plays important roles in FPB release and in lateral aggregation of protofibrils

BACKGROUND AND OBJECTIVES

Analysis of dysfibrinogens has improved our understanding of molecular defects and their effects on the function of intact fibrinogen. To eliminate the influence of plasma heterozygous molecules, we synthesized and analyzed recombinant-variant fibrinogens.

METHODS

We synthesized two recombinant-variant fibrinogens with a single amino acid substitution at the 15Gly residue in the Bbeta-chain: namely, Bbeta15Cys and Bbeta15Ala.

RESULTS

Western blotting analysis of purified fibrinogen revealed the existence of a small amount of a dimeric form only for Bbeta15Cys fibrinogen. For Bbeta15Cys fibrinogen, functional analysis indicated (a) no thrombin-catalyzed fibrinopeptide B (FPB) release and (b) markedly impaired lateral aggregation in thrombin- and reptilase-catalyzed fibrin polymerizations. For Bbeta15Ala fibrinogen, such analysis indicated slight impairments of both thrombin-catalyzed FPB release and lateral aggregation in thrombin-catalyzed fibrin polymerization, but nearly normal lateral aggregation in reptilase-catalyzed fibrin polymerization. These impaired lateral aggregations were accompanied by thinner fibrin fiber diameters (determined by scanning electron microscopy of the corresponding fibrin clots).

CONCLUSION

We conclude that a region adjacent to Bbeta15Gly plays important roles in lateral aggregation not only in desA fibrin polymerization, but also in desAB fibrin polymerization, and we speculate that the marked functional differences between Bbeta15A and Bbeta15C fibrinogens in FPB release and fibrin polymerization might not only be due to the presence of a substituted cysteine residue in Bbeta15C fibrinogen, but also to the existence of disulfide-bonded forms. Finally, our data indicate that the Bbeta15Gly residue plays important roles in FPB release and lateral aggregation of protofibrils.

Fibrinogen Philadelphia, a hypodysfibrinogenemia characterized by abnormal polymerization and fibrinogen hypercatabolism due to gamma S378P mutation

Fibrinogen Philadelphia, a hypodysfibrinogenemia described in a family with a history of bleeding, is characterized by prolonged thrombin time, abnormal fibrin polymerization, and increased catabolism of the abnormal fibrinogen. Turbidity studies of polymerization of purified fibrinogen under different ionic conditions reveal a reduced lag period and lower final turbidity, indicating more rapid initial polymerization and impaired lateral aggregation. Consistent with this, scanning and transmission electron microscopy show fibers with substantially lower average fiber diameters. DNA sequence analysis of the fibrinogen genes A, B, and G revealed a T>C transition in exon 9 resulting in a serine-to-proline substitution near the gamma chain C-terminus (S378P). The S378P mutation is associated with fibrinogen Philadelphia in this kindred and was not found in 10 controls. This region of the gamma chain is involved in fibrin polymerization, supporting this as the polymerization defect causing the mutation. Thus, this abnormal fibrinogen is characterized by 2 unique features: (1) abnormal polymerization probably due to a major defect in lateral aggregation and (2) hypercatabolism of the mutant protein. The location, nature, and unusual characteristics of this mutation may add to our understanding of fibrinogen protein interactions necessary for normal catabolism and fibrin formation.

John Ferry and the mechanical properties of cross-linked fibrin

This article describes the role John Ferry played in relating the location of cross-linked gamma-chains in fibrin fibrils to the mechanical properties of fibrin clot.

Comparison of thrombin-catalyzed fibrin polymerization and factor XIIIa-catalyzed cross-linking of fibrin among three recombinant variant fibrinogens, gamma 275C, gamma 275H, and gamma 275A

BACKGROUND AND OBJECTIVES

We have previously reported that recombinant gamma 275Cys fibrinogen exhibits a marked impairment of functions as well as aberrant fibrin clot and bundle structures, as compared with wild-type, gamma 275Arg, and plasma fibrinogen from a heterozygous proband. Since gamma Arg275His mutations have also been reported in 10 families, we synthesized recombinant gamma 275His fibrinogen and gamma 275Ala fibrinogen (as a control) and analyzed and compared them with gamma 275Cys and gamma 275Arg.

METHODS

A variant gamma-chain expression plasmid was transfected into Chinese hamster ovary cells expressing normal human fibrinogen A alpha- and B beta-chains. After purification of the recombinant variant fibrinogens, we performed functional analyzes for thrombin-catalyzed fibrin polymerization and factor XIIIa (FXIIIa)-catalyzed gamma-gamma dimer formation from fibrin or fibrinogen and also ultrastructural analysis of fibrin clots and bundles.

RESULTS

By comparison with both gamma 275His and gamma 275Ala fibrinogens, recombinant gamma 275Cys fibrinogen exhibited a more impaired gamma-gamma dimer formation from fibrin or fibrinogen, a more aberrant fibrin clot structure, and thicker fibers in fibrin bundles. In 1 : 1 mixtures of gamma 275Arg and gamma 275Cys fibrinogens or gamma 275Arg and gamma 275His fibrinogens, thrombin-catalyzed fibrin polymerization and both fibrin clot and fiber structures showed some compensation (as compared with gamma 275Cys or gamma 275His alone).

CONCLUSION

These results strongly suggest that an amino acid substitution of gamma 275Arg alone disrupts D:D interactions in thrombin-catalyzed fibrin polymerization and the formation of fibrin bundles and fibrin clots. Moreover, the existence of a subsequent disulfide-linked Cys in gamma 275C fibrinogen augments the impairment caused by a His or Ala substitution.

Recombinant fibrinogen, gamma275Arg-->Cys, exhibits formation of disulfide bond with cysteine and severely impaired D:D interactions

BACKGROUND AND OBJECTIVES

Analysis of dysfibrinogens has provided useful information aiding our understanding of molecular defects in fibrin polymerization. We have already reported impaired fibrin polymerization in a variant fibrinogen (gammaArg275Cys), the Cys being located in the D:D interface. Since this substitution occurred in a heterozygous individual, interpretation of the functional analysis was complicated. We tried to resolve this complication by synthesizing a recombinant variant fibrinogen.

METHODS

A variant gamma-chain expression plasmid was transfected into Chinese hamster ovary cells expressing normal human fibrinogen Aalpha- and Bbeta-chains. The recombinant variant fibrinogen (gamma275C) was purified using an immunoaffinity column, and we compared its structure and functions with those of normal recombinant fibrinogen (gamma275R) and plasma variant fibrinogen.

RESULTS

Mass analyses showed the existence of disulfide-linked Cys in both patient and recombinant variant fibrinogens. Functional analyses indicated that both fibrin polymerization and gamma-gamma dimer formation were markedly impaired in the variant fibrinogen. The impairments were much more pronounced in gamma275C than in plasma variant fibrinogen. In addition, scanning electron microscopic observation of fibrin clots made from gamma275C revealed less dense fibrin fiber bundles and larger fiber diameter than in those made from gamma275R, and also the existence of many aberrant fibrin fibers with tapered ends.

CONCLUSIONS

These results indicate that gammaArg275 has an important residue affecting the structure and function of the gamma-chain C-terminal domain. However, the variant D:D interface can interact with that of the normal fibrinogen existing in a heterozygous patient with dysfibrinogenemia.

Substitution of the gamma-chain Asn308 disturbs the D:D interface affecting fibrin polymerization, fibrinopeptide B release, and FXIIIa-catalyzed cross-linking

Crystallographic structures indicate that gamma-chain residue Asn308 participates in D:D interactions and indeed substitutions of gammaAsn308 with lysine or isoleucine have been identified in dysfibrinogens with impaired polymerization. To probe the role of Asn308 in polymerization, we synthesized 3 variant fibrinogens: gammaAsn308 changed to lysine (gammaN308K), isoleucine (gammaN308I), and alanine (gammaN308A). We measured thrombin-catalyzed polymerization by turbidity, fibrinopeptide release by high-performance liquid chromatography, and factor XIIIa-catalyzed cross-linking by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the absence of added calcium, polymerization was clearly impaired with all 3 variants. In contrast, at 0.1 mM calcium, only polymerization of gammaN308K remained markedly abnormal. The release of thrombin-catalyzed fibrinopeptide B (FpB) was delayed in the absence of calcium, whereas at 1 mM calcium FpB release was delayed only with gammaN308K. Factor XIIIa-catalyzed gamma-gamma dimer formation was delayed with fibrinogen (in absence of thrombin), whereas with fibrin (in presence of thrombin) gamma-gamma dimer formation of only gammaN308K was delayed. These data corroborate the recognized link between FpB release and polymerization. They show fibrin cross-link formation likely depends on the structure of protofibrils. Together, our results show substitution of Asn308 with a hydrophobic residue altered neither polymer formation nor polymer structure at physiologic calcium concentrations, whereas substitution with lysine altered both.

Fibrinogen gamma chain functions

This review covers the functional features of the fibrinogen gamma chains including their participation in fibrin polymerization and cross-linking, their role in the initiation of fibrinolysis, their binding and regulation of factor XIII activity, their interactions with platelets and other cells, and their role in mediating thrombin binding to fibrin, a thrombin inhibitory function termed 'antithrombin I'.

Structure and function of human fibrinogen inferred from dysfibrinogens

Fibrinogen is a 340-kDa plasma protein that is composed of two identical molecular halves, each consisting of three non-identical subunit polypeptides designated as A alpha, B beta- and gamma-chains held together by multiple disulfide bonds. Fibrinogen has a trinodular structure, i.e., one central E domain comprizing the amino-terminal regions of paired individual three polypeptides, and two identical outer D domains. These three nodules are linked by two coiled-coil regions [1,2]. After activation with thrombin, a tripeptide segment consisting of Gly-Pro-Arg is exposed at the amino-terminus of each alpha-chain residing at the center of the E domain and combines with its complementary binding site, called the 'a' site, residing in the carboxyl-terminal region of the gamma-chain in the outer D domain of another molecule. By crystallographic analysis [3], the alpha-amino group of alpha Gly-1 is shown to be juxtaposed between the carboxyl group of gamma Asp-364 and the carboxyamide of Gln-329 in the 'a' site. Half molecule-staggered, double-stranded fibrin protofibrils are thus formed [4,5]. Upon abutment of two adjacent D domains on the same strand, D-D self association takes place involving Arg-275, Tyr-280 and Ser-300 of the gamma-chain on the surface of the abutting two D domains [3]. Thereafter, carboxyl-terminal regions of the fibrin a-chains are thought to be untethered and interact with those of other protofibrils leading to the formation of thick fibrin bundles and interwoven networks after appropriate branching [6-9]. Although many enigmas still remain regarding the mechanisms of these molecular interactions, fibrin assembly proceeds in a highly ordered fashion. In my talk, I would like to discuss these molecular interactions of fibrinogen and fibrin based on the up-date data provided by analyses of normal as well as hereditary dysfibrinogens, particularly in the latter by introducing representative molecules at each step of fibrin clot formation.

Disintegration and reorganization of fibrin networks during tissue-type plasminogen activator-induced clot lysis

In this study, we investigated tissue-type plasminogen activator (tPA)-induced lysis of glutamic acid (glu)-plasminogen-containing or lysine (lys)-plasminogen-containing thrombin-induced fibrin clots. We measured clot development and plasmin-mediated clot disintegration by thromboelastography, and used scanning electron microscopy (SEM) to document the structural changes taking place during clot formation and lysis. These events occurred in three overlapping stages, which were initiated by the addition of thrombin, resulting first in fibrin polymerization and clot network organization (Stage I). Autolytic plasmin cleavage of glu-plasminogen at lys-77 generates lys-plasminogen, exposing lysine binding sites in its kringle domains. The presence of lys-plasminogen within the thrombin-induced fibrin clot enhanced network reorganization to form thicker fibers as well as globular complexes containing fibrin and lys-plasminogen having a greater level of turbidity and a higher elastic modulus (G) than occurred with thrombin alone. Lys-plasminogen or glu-plasminogen that had been incorporated into the fibrin clot was activated to plasmin by tPA admixed with the thrombin, and led directly to clot disintegration (Stage II) concomitant with fibrin network reorganization. The onset of Stage III (clot dissolution) was signaled by a sustained secondary rise in turbidity that was due to the combined effects of lys-plasminogen presence or its conversion from glu-plasminogen, plus clot network reorganization. SEM images documented dynamic structural changes in the lysing fibrin network and showed that the secondary turbidity rise was due to extensive reorganization of severed fibrils and fibers to form wide, occasionally branched fibers. These degraded structures contributed little, if anything, to the structural integrity of the residual clot, and eventually collapsed completely during the course of progressive clot dissolution. These results provide new perspectives on the major structural events that occur in the fibrin clot matrix during fibrinolysis.

The structure and biological features of fibrinogen and fibrin

Fibrinogen and fibrin play important, overlapping roles in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, and neoplasia. These events are regulated to a large extent by fibrin formation itself and by complementary interactions between specific binding sites on fibrin(ogen) and extrinsic molecules including proenzymes, clotting factors, enzyme inhibitors, and cell receptors. Fibrinogen is comprised of two sets of three polypeptide chains termed A alpha, B beta, and gamma, that are joined by disulfide bridging within the N-terminal E domain. The molecules are elongated 45-nm structures consisting of two outer D domains, each connected to a central E domain by a coiled-coil segment. These domains contain constitutive binding sites that participate in fibrinogen conversion to fibrin, fibrin assembly, crosslinking, and platelet interactions (e.g., thrombin substrate, Da, Db, gamma XL, D:D, alpha C, gamma A chain platelet receptor) as well as sites that are available after fibrinopeptide cleavage (e.g., E domain low affinity non-substrate thrombin binding site); or that become exposed as a consequence of the polymerization process (e.g., tPA-dependent plasminogen activation). A constitutive plasma factor XIII binding site and a high affinity non-substrate thrombin binding site are located on variant gamma' chains that comprise a minor proportion of the gamma chain population. Initiation of fibrin assembly by thrombin-mediated cleavage of fibrinopeptide A from A alpha chains exposes two EA polymerization sites, and subsequent fibrinopeptide B cleavage exposes two EB polymerization sites that can also interact with platelets, fibroblasts, and endothelial cells. Fibrin generation leads to end-to-middle intermolecular Da to EA associations, resulting in linear double-stranded fibrils and equilaterally branched trimolecular fibril junctions. Side-to-side fibril convergence results in bilateral network branches and multistranded thick fiber cables. Concomitantly, factor XIII or thrombin-activated factor XIIIa introduce intermolecular covalent epsilon-(gamma glutamyl)lysine bonds into these polymers, first creating gamma dimers between properly aligned C-terminal gamma XL sites, which are positioned transversely between the two strands of each fibrin fibril. Later, crosslinks form mainly between complementary sites on alpha chains (forming alpha-polymers), and even more slowly among gamma dimers to create higher order crosslinked gamma trimers and tetramers, to complete the mature network structure.

Hereditary disorders of fibrinogen

Fibrinogen, a 340-kDa plasma protein, is composed of two identical molecular halves each consisting of three non-identical A alpha-, B beta- and gamma-chain subunits held together by multiple disulfide bonds. Fibrinogen is shown to have a trinodular structure; that is, one central nodule, the E domain, and two identical outer nodules, the D-domains, linked by two coiled-coil regions. After activation with thrombin, a pair of binding sites comprising Gly-Pro-Arg is exposed in the central nodule and combines with its complementary binding site a in the outer nodule of another molecules. By using crystallographic analysis, the alpha-amino group of alpha Gly-1 is shown to be juxtaposed between gamma Asp-364 and gamma Asp-330, and guanidino group of alpha Arg-3 between the carboxyl group of gamma Asp-364 and gamma Gln-329 in the a site. Half molecule-staggered, double-stranded protofibrils are thus formed. Upon abutment of two adjacent D domains on the same strand, D-D self association takes place involving Arg-275, Tyr-280, and Ser-300 of the gamma-chain on the surface of the abutting two D domains. Thereafter, carboxyl-terminal regions of the alpha-chains are untethered and interact with those of other protofibrils leading to the formation of thick fibrin bundles and networks. Although many enigmas still remain concerning the exact mechanisms of these molecular interactions, fibrin assembly proceeds in a highly ordered fashion. In this review, these molecular interactions of fibrinogen and fibrin are discussed on the basis of the data provided by hereditary dysfibrinogens on introducing representative molecules at each step of fibrin clot formation.

Fibrinogen bellingham: a gamma-chain R275C substitution and a beta-promoter polymorphism in a thrombotic member of an asymptomatic family

Congenital dysfibrinogenemia is a rare cause of unexplained thrombosis. However, most individuals with dysfibrinogenemia are asymptomatic, suggesting that co-morbid factors contribute to thrombo-embolic events. The potential roles of additional genetic or acquired prothrombotic risk factors are poorly understood because detailed family studies are lacking. Herein, we describe a family whose propositus was a young Caucasian man with recurrent venous thrombo-emboli and dysfibrinogenemia due to heterozygosity for an Arg-->Cys substitution at residue 275 in the gamma-chain. The only additional thrombophilic abnormality found in the proband was heterozygosity for a G/A transition at position -455 in the fibrinogen beta-chain promoter; a genotype associated with high acute phase levels of fibrinogen. The proband's father, who died of a cerebral artery thrombosis, carried the gammaR275C substitution but not the beta-promoter -455 variant. Among 14 living relatives, eight were heterozygous for one or the other mutation and only one, a 21-year-old niece, was dually affected. None had suffered bleeding or thrombosis. In vitro studies of the proband's purified fibrinogen revealed markedly abnormal thrombin-catalyzed polymerization and delayed fibrin clot lysis by tPA-activated plasmin. We hypothesize that the gammaR275C substitution predisposes to thrombosis by generating clots that are relatively resistant to fibrinolysis. The clinical risk is low, however, in the absence of an additional thrombophilic mutation. The beta-promoter variant could, theoretically, contribute to this risk by augmenting expression of the dysfibrinogen under conditions of stress. Like the common hereditary thrombophilias, heterozygous familial dysfibrinogenemia induces thrombosis in the setting of multiple prothrombotic influences.

Polymerization of rod-like macromolecular monomers studied by stopped-flow, multiangle light scattering: set-up, data processing, and application to fibrin formation

Many biological supramolecular structures are formed by polymerization of macromolecular monomers. Light scattering techniques can provide structural information from such systems, if suitable procedures are used to collect the data and then to extract the relevant parameters. We present an experimental set-up in which a commercial multiangle laser light scattering photometer is linked to a stopped-flow mixer, allowing, in principle, the time-resolved extrapolation of the weight-average molecular weight M(w) and of the z-average square radius of gyration <R(g)(2)>(z) of the polymers from Zimm-like plots. However, if elongated structures are formed as the polymerization proceeds, curved plots rapidly arise, from which M(w) and <R(g)(2)>(z) cannot be recovered by linear fitting. To verify the correctness of a polynomial fitting procedure, polydisperse collections of rod-like or worm-like particles of different lengths, generated at various stages during bifunctional polycondensations of rod-like macromolecular monomers, were considered. Then, the angular dependence of their time-averaged scattered intensity was calculated in the Rayleigh-Gans-Debye approximation, with random and systematic noise also added to the data. For relatively narrow size distributions, a third-degree polynomial fitting gave satisfactory results across a broad range of conversion degrees, yielding M(w) and <R(g)(2)>(z) values within 2% and no greater than 10-20%, respectively, of the calculated values. When more broad size distributions were analyzed, the procedure still performed well for semiflexible polymers, but started to seriously underestimate both M(w) and <R(g)(2)>(z) when rigid rod-like particles were analyzed, even at relatively low conversion degrees. The data were also analyzed in the framework of the Casassa approximation, from which the mass per unit length of the polymers can be derived. These procedures were applied to a set of data taken on the early stages of the thrombin-catalyzed polymerization of fibrinogen, a rod-like macromolecule approximately 50 nm long. The polymers, grown in the absence of Ca(2+) by rate-limiting amounts of thrombin, appeared to be characterized by a much broader size distribution than the one expected for a classical Flory bifunctional polycondensation, and they seem to behave as relatively flexible worm-like double-stranded chains. Evidence for the formation of fibrinogen-fibrin monomer complexes is also inferred from the time dependence of the mass/length ratio. However, our data are also compatible with the presence of limited amounts of single-stranded structures in the very early stages, either as a secondary, less populated pathway, or as transient intermediates to the classical double-stranded fibrils.

Fibrinogen Niigata With Impaired Fibrin Assembly: An Inherited Dysfibrinogen With a Bβ Asn-160 to Ser Substitution Associated With Extra Glycosylation at Bβ Asn-158

A novel BβAsn-160 (TAA) to Ser (TGA) substitution has been identified in fibrinogen Niigata derived from a 64-year-old asymptomatic woman, who is heterozygotic for this abnormality. The mutation creates an Asn-X-Ser–type glycosylation sequence, and a partially sialylated biantennary oligosaccharide was linked to the BβAsn-158 residue. The functional abnormality was attributed to delayed lateral association of normally formed double-stranded protofibrils based on normal cross-linking of fibrin γ-chains and tissue-type plasminogen activator-catalyzed plasmin generation by polymerizing fibrin monomers. Enzymatic removal of all the N-linked oligosaccharides from fibrinogen Niigata accelerated fibrin monomer polymerization that reached the level of untreated normal fibrin monomers, but the thrombin time was prolonged from 18.2 seconds to 113 seconds (normal: 11.2 seconds to 8.9 seconds). By scanning electron micrographic analysis, Niigata fibrin fibers were found to be more curvilinear than normal fibrin fibers. After deglycosylation, Niigata fibers became straight being similar to untreated normal fibrin fibers, whereas normal deglycosylated fibrin appeared to be less-branched than untreated normal or deglycosylated Niigata fibrin. Although normal and Niigata fibrins were similar to each other in permeation and compaction studies, deglycosylated normal and Niigata fibrins had much higher permeability and compaction values, indicating that deglycosylation had brought about the formation of more porous networks. The enzymatic deglycosylation necessitates an Asn to Asp change at position Bβ-158 that is responsible for reducing the fiber thickness because of either local repulsive forces or steric hindrance in the coiled-coil region.

Fibrinogen Niigata With Impaired Fibrin Assembly: An Inherited Dysfibrinogen With a Bβ Asn-160 to Ser Substitution Associated With Extra Glycosylation at Bβ Asn-158

A novel BβAsn-160 (TAA) to Ser (TGA) substitution has been identified in fibrinogen Niigata derived from a 64-year-old asymptomatic woman, who is heterozygotic for this abnormality. The mutation creates an Asn-X-Ser–type glycosylation sequence, and a partially sialylated biantennary oligosaccharide was linked to the BβAsn-158 residue. The functional abnormality was attributed to delayed lateral association of normally formed double-stranded protofibrils based on normal cross-linking of fibrin γ-chains and tissue-type plasminogen activator-catalyzed plasmin generation by polymerizing fibrin monomers. Enzymatic removal of all the N-linked oligosaccharides from fibrinogen Niigata accelerated fibrin monomer polymerization that reached the level of untreated normal fibrin monomers, but the thrombin time was prolonged from 18.2 seconds to 113 seconds (normal: 11.2 seconds to 8.9 seconds). By scanning electron micrographic analysis, Niigata fibrin fibers were found to be more curvilinear than normal fibrin fibers. After deglycosylation, Niigata fibers became straight being similar to untreated normal fibrin fibers, whereas normal deglycosylated fibrin appeared to be less-branched than untreated normal or deglycosylated Niigata fibrin. Although normal and Niigata fibrins were similar to each other in permeation and compaction studies, deglycosylated normal and Niigata fibrins had much higher permeability and compaction values, indicating that deglycosylation had brought about the formation of more porous networks. The enzymatic deglycosylation necessitates an Asn to Asp change at position Bβ-158 that is responsible for reducing the fiber thickness because of either local repulsive forces or steric hindrance in the coiled-coil region.

The location of the carboxy-terminal region of gamma chains in fibrinogen and fibrin D domains

Elongated fibrinogen molecules are comprised of two outer "D" domains, each connected through a "coiled-coil" region to the central "E" domain. Fibrin forms following thrombin cleavage in the E domain and then undergoes intermolecular end-to-middle D:E domain associations that result in double-stranded fibrils. Factor XIIIa mediates crosslinking of the C-terminal regions of gamma chains in each D domain (the gammaXL site) by incorporating intermolecular epsilon-(gamma-glutamyl)lysine bonds between amine donor gamma406 lysine of one gamma chain and a glutamine acceptor at gamma398 or gamma399 of another. Several lines of evidence show that crosslinked gamma chains extend "transversely" between the strands of each fibril, but other data suggest instead that crosslinked gamma chains can only traverse end-to-end-aligned D domains within each strand. To examine this issue and determine the location of the gammaXL site in fibrinogen and assembled fibrin fibrils, we incorporated an amine donor, thioacetyl cadaverine, into glutamine acceptor sites in fibrinogen in the presence of XIIIa, and then labeled the thiol with a relatively small (0.8 nm diameter) electron dense gold cluster compound, undecagold monoaminopropyl maleimide (Au11). Fibrinogen was examined by scanning transmission electron microscopy to locate Au11-cadaverine-labeled gamma398/399 D domain sites. Seventy-nine percent of D domain Au11 clusters were situated in middle to proximal positions relative to the end of the molecule, with the remaining Au11 clusters in a distal position. In fibrin fibrils, D domain Au11 clusters were located in middle to proximal positions. These findings show that most C-terminal gamma chains in fibrinogen or fibrin are oriented toward the central domain and indicate that gammaXL sites in fibrils are situated predominantly between strands, suitably aligned for transverse crosslinking.

Electrospray ionization mass spectrometry identification of fibrinogen Banks Peninsula (gamma280Tyr-->Cys): a new variant with defective polymerization

Fibrinogen Banks Peninsula was identified in the mother of a patient referred for investigation following recurrent epistaxis. Coagulation tests revealed prolonged thrombin and reptilase times and a decreased functional fibrinogen level. Thrombin-catalysed release of fibrinopeptides A and B was normal, and no abnormalities were detected by DNA sequencing of the regions encoding the thrombin cleavage sites in the Aalpha and Bbeta genes. Reducing SDS-PAGE and reverse-phase HPLC analysis of purified fibrinogen chains were normal, as was electrospray ionization mass spectrometry (ESI-MS) analysis of isolated Aalpha and Bbeta chains. However ESI-MS revealed a mass of 48345 D for the isolated gamma chains, 31 D less than the measured mass of control chains (48376 D). Since normal and abnormal gamma chains were not resolved, this implies a 60-62 D mass decrease in 50% of the molecules. A 60 D decrease was confirmed when DNA sequencing indicated heterozygosity for a mutation of Tyr-->Cys at codon 280 of the gamma chain gene. Fibrin monomer polymerization revealed a delayed lag phase and reduced final turbidity and although factor XIIIa crosslinking of fibrinogen was normal, it is likely that this delay is due to impaired D:D self association. Recent crystallographic studies show residues gamma280 and gamma275 make contact across the D:D interface, suggesting a similar mechanism for the polymerization defects in fibrinogens Banks Peninsula and Tokyo II (gamma275Arg-->Cys).